1. Field of the Invention
The invention relates to a steer-by-wire steering system for a vehicle, having a manual steering device, in particular a steering wheel, connected to a steering column, and having a steering wheel actuator acting on the steering column, the steering wheel actuator having a rotor, connected to the steering column in a manner fixed against relative rotation, and a stator.
2. Description of the Prior Art
Steer-by-wire steering systems are distinguished in that in normal operation, there is no direct mechanical connection between the steering wheel and the steered wheels. Instead, the steering desired by the driver is detected via rotary angle sensors at the steering column and processed by a control unit, which transmits control signals accordingly to a steering actuator acting on the steered wheels of the vehicle.
A steering wheel actuator, via a moment, simulates the contact with the road for the driver. To that end, relatively low moment levels are required (approximately 5 Nm). For this reason, the electric motor that generates the moment can be integrated as a direct drive mechanism into the actuator, without an additional step-up gear. This makes a very good steering feel possible, with little fluctuation in moment and little noise development.
If higher moments are to be simulated for the driver, for instance by means of a steering stop or curb stop of the wheels, however, this cannot be done with that kind of electric motor without a gear. Since the steering stop, which in conventional steering systems is predetermined by the steering gear does not create any limitations to the rotary motion of the steering wheel in steer-by-wire steering systems, it is necessary to provide a separate steering stop for the steering wheel or steering column. This is necessary to prevent a flat spiral spring, for instance, in the steering column, which is required for actuating the horn, tripping an airbag, and/or actuating an automatic transmission, from being rotated excessively. If the flat spiral spring is rotated excessively, it becomes damaged. A curb stop can also be simulated by means of the rotary angle limitation of the steering column.
There are also steer-by-wire steering systems that have a so-called fallback plane. In terms of the present invention, fallback plane means a conventional mechanical connection between the steering wheel and the steering actuator that is activated if the steer-by-wire steering system fails. In the steer-by-wire mode, the mechanical connection between the steering wheel and the steering actuator is disconnected by a disengageable clutch, while for activating the fallback plane, the disengageable clutch is closed.
From German Patent Disclosure DE 43 30 658 A1, a steering wheel block for motor vehicles is known that uses clamping bodies.
The object of the invention is to furnish a steer-by-wire steering system braking device that is compact in structure, can be produced economically, and moreover has low energy consumption in the steer-by-wire mode. Moreover, the braking device should be triggerable simply and reliably.
In conjunction with the invention, the terms “clutch” and “braking device” differ in that a clutch transmits rotary motions and torques, while a braking device in the sense of the invention transmits only torque, since part of the braking device is connected to the vehicle in a manner fixed against relative rotation.
According to the invention, in a steer-by-wire steering system for a vehicle, having a manual steering device, in particular a steering wheel, connected to a steering column, and having a steering wheel actuator acting on the steering column, the steering wheel actuator having a rotor, connected to the steering column in a manner fixed against relative rotation, and a stator, this object is attained in that there is a braking device acting on the steering column; and that the braking device is actuated as a function of the torque transmitted from the stator to the steering column.
According to the invention, this object is also attained by a steer-by-wire steering system for a vehicle, having a manual steering device, in particular a steering wheel, connected to a steering column, having a clutch that couples a first portion to a second portion of a steering column, and having a steering wheel actuator acting on the steering column, the steering wheel actuator having a rotor, connected to the steering column in a manner fixed against relative rotation, and a stator, in that there is a clutch acting on the steering column; and that the clutch is actuated as a function of the torque transmitted from the stator to the steering column.